It is conventional to dip coat and fuse a plasticized polyvinyl chloride coating (referred to as fused polyvinyl chloride) upon open structured metal articles (commonly referred to as expanded metals) such as commonly used to protectively coat grated metal outdoor fixtures (e.g. bench seats and tops, waste receptacles, etc.). Dip coating is particularly desirable for many application since it permits the formation of very thick coatings. The dip coating typically comprises preheating a primed and cleaned expanded metal article to a bath immersion temperature, immersing the expanded article into a heated bath of unfused plasticized polyvinyl chloride, removing the metal article from the bath, allowing excessive dip coated polyvinyl chloride material to drain from the article to provide an article coated with an unfused plasticized polyvinyl chloride coating and fusing the polyvinyl chloride coating onto the metal article by passing the polyvinyl chloride coated article through a baking oven.
Open structured or expanded metal articles characteristically have only about 15% or less surface area of a closed structured form which allows such expanded metal articles to be easily and uniformly coated with a plasticized polyvinyl chloride coating material by dip coating. Articles such as metal grates and other highly porous metallic objects which typically contain a high percentage (e.g. greater than a major portion) of open structured coating surface (versus a major solid structure surface area) may accordingly be easily and economically dip coated with an uniform coating of the fused plasticized polyvinyl chloride. Unfortunately, it is not feasible under the existing technology to uniformly coat unexpanded metal articles having planar surface areas in which its centroid is typically six inches or more removed from its planar edge (i.e. its interior portion) and a substantial portion (e.g. more than 50% of its total surface area constitutes a solid material) of the structure therewithin constitutes a solid structure.
In the dip coating process, a desired objective is to create a relatively thick coating which affords greater protection to the coated article against wear and tear as well as weathering. Thicker coatings generally dictate the need to use the more viscous unfused plasticized polyvinyl chloride coating materials in the coating operation. Unfortunately, the more viscous material accentuates the propensity of the coating material to form a non-uniform coating upon the non-expanded areas of the substrate. Equally as perplexing is the inability to produce a coated article having exceptional resistance against peeling.
Attempts to dip coat such solid or unexpanded metallic articles with a fused plasticized polyvinyl chloride coating results in a wrinkled coating exhibiting especially poor adherence to the metallic object. Consequently, abrasive or peeling forces causes the fused coating to be readily separated or peeled from its solid surface. This problem is further compounded by vandalism in which the vandals, being aware that the fused coating may be readily peeled or separated from the coated substrate, will intentionally peel or cut the coating, thus exposing the coated substrate to premature rusting and weathering. Another persistent problem arises by the presence of tear-shaped drops which prominently arise along the peripheral borders or edges of dip coated articles. Under existing technology, it is virtually impossible to obtain a fused dip coating of a substantially uniform layer or coating thickness upon such solid objects. The non-uniformity in fused coating may also be reflected in a wrinkled and motley or pitted surface with pronounced fused droplets accruing along the peripheral edges of the dip coated article. These factors create an unsightly and inferior product of substantially reduced commercial value.